The Mammalian Respiratory System

Mammalian Respiratory System Mammals (yes that includes humans – Gifty) have a very complex respiratory system that includes: Breathing = taking air into the lungs (inspiration), and forcing air out of the lungs (expiration) External respiration = the exchange of O2 and CO2 between air and blood Internal respiration = the exchange of O2 and CO2 between blood and the cells of the surrounding tissue Cellular respiration = the complex series of chemical reactions in the mitochondria of cells that uses O2 to produce ATP and CO2

The Respiratory Tract Mammalian lungs must be shielded within the body: To prevent water loss – the respiratory surface must be moist To guard against damage – lungs are delicate, fragile structures with many folds and fine membranes Protected deep within the body by the bone and muscular structure of the thoracic cavity. Therefore, we need a passageway to allow air to move from the external environment to the respiratory surface deep inside the body

Upper Respiratory Tract

The Upper Respiratory Tract Air first enters through the nostril cavity Or in humans and many other animals, also through the mouth Air passes through hollow nasal passages which contain thin bones, called turbinates, that hang suspended from the nasal chambers Increases the surface area of the nasal chambers and secrete mucus to moistens the incoming air The cell linings of the nasal chambers and the turbinate bones are well supplied with capillaries warm the incoming air increase its relative humidity Serves to protect the delicate lung tissue

Turbinates

Upper Respiratory Tract Air then passes through the pharynx, the glottis, and the larynx: The pharynx connects the mouth and nasal cavity to the larynx and esophagus The glottis is the opening of the trachea, the passageway that conducts air to the lungs. This opening is protected by the epiglottis The pharynx is the dividing point between the trachea (air) and the esophagus (food)

Upper Respiratory Tract The larynx, or “voice box,” contains the two folded structures of the vocal cords. When you breathe normally, there is a large gap between the two cords. When you prepare to speak, muscles around the larynx contract, bringing the cords closer together. The passage of air through this narrower space causes the cords to vibrate, producing a sound. The pitch of the sound varies with the length of the cords: a long cord produces a low sound a shorter cord produces a higher sound. At puberty, the vocal cords of males grow quickly

Upper Respiratory Tract After the larynx, air goes down the flexible tube of the trachea. The trachea is supported in part by semicircular cartilage rings. Prevent the trachea from collapsing The nasal and other passages of the upper respiratory tract are lined with ciliated cells that secrete mucus. Traps foreign particles such as dust and bacteria The cilia helps to propel this material back into the nose and throat where it can be expelled by coughing or sneezing. So why do we cough/sneeze more when we’re sick?

The Lower Respiratory Tract The trachea branches into two smaller passageways called bronchi (singular bronchus) One bronchus enters each lung Each bronchus subdivides many times to produce a network of finer and finer tubes called bronchioles. the bronchi and bronchioles are also lined with a ciliated mucous membrane.

Lower Respiratory Tract Each bronchiole ends in a grape-like cluster of tiny sacs called alveoli (singular alveolus). In the moist alveoli is where the actual exchange of gases takes place The wall of each alveoli is one cell thick and is adjacent to a network of tiny capillaries These capillaries are the site for the exchange of oxygen and carbon dioxide in the body. Most of the exchange of gases takes place through simple diffusion, but facilitated diffusion accounts for some (possibly as much as 30%) This allows the blood to take up oxygen more quickly than would otherwise be possible.

Lower Respiratory Tract In the spaces between the individual structures of the respiratory tract is elastic connective tissue Keeps the alveoli and bronchi in a relatively permanent position The alveoli are also lined with a lubricating film that helps to keep them from collapsing

Lower Respiratory Tract Each lung is divided into lobes. The right lung has 3 lobes The left lung has only 2. Why? To accommodate the heart The lungs themselves are enveloped in layers of tissue called pleura. A flexible membrane that contains the lungs while still allowing them to expand and contract during inspiration and expiration Each pleuron is made up of two layers separated by a thin film of lubricating fluid